1. Field of the Invention
This invention relates to hydro-cyclones of the type conventionally used in processing and classifying solids or solid/fluid phases. Specifically, this invention relates to dual hydro-cyclone systems which are structured to provide higher processing efficiencies through selectively, axially adjustable contact means and other novel structures.
2. Description of the Related Art
Grinding classification in the processing of ore is of great importance because an effective classification increases the capacity of the equipment and prevents material over-grinding. The current grinding circuits mainly use hydro-cyclones as classification equipment. The following are some of the main advantages of hydrocyclones:
1. They are small pieces of equipment with a high specific capacity, low residence time and low operational inertia, which is advantageous for the automatic control of grinding circuits.
2. They have a very simple structure, which in turn translates into low investment, operation and maintenance costs.
3. They are all-purpose pieces of equipment; i.e., they may be used as classifiers, thickeners, slime separators, pre-concentrators, solids scrubbers and fluid degassers.
4. They apply a high shear stress on the pulp feed and may thus be used for breaking agglomerates and classifying non-Newtonian pulps, which decrease their viscosity with an increased shear rate.
However, hydro-cyclones present the following disadvantages:
a) Although they are all-purpose pieces of equipment as to their application, they allow little modification of their characteristics in the event of a dramatic change in the conditions of the ore fed into the plant.
b) Hydro-cyclones are not specifically designed for a particular case or application, as they are usually manufactured in series. At most, they have a modular design to facilitate their assembly in such a way as to meet particular needs. Adaptation of these modules or equipment to meet particular needs is made empirically through tests at the industrial site itself. Obviously, this type of procedure is expensive and time consuming, but it is the only accurate method currently available.
c) One of their main disadvantages is their low efficiency. Their separation efficiency is given by three parameters: the short circuit, the cut-off size and cut-off sharpness or sharpness rate. The first parameter quantifies the rate of unclassified output of the cyclone""s feed flow, which translates into lower throughput of the grinding circuit. The cut-off sharpness quantifies separation quality between coarse and fine during classification; this not only has an effect on its throughput and quality of the product, but also on the cut-off size.
Due to their hydrodynamic operational characteristics, hydro-cyclones used in grinding circuits of process plants have high shortcircuit rates, sometimes over 40%. One way of solving this problem is to use more diluted pulps and more concentrated discharge conditions. This solution is quite difficult to apply in high-capacity process plants because dilution requires an increased flow of pulp and also because the concentration process that follows the grinding process requires pulp with a controlled content of solids. Thus, most process plants operate under conditions that result in low efficiency of the hydro-cyclones, since this problem has not been satisfactorily solved. On the other hand, the hydro-cyclone""s cut-off sharpness is low as the cut-off under size contains coarse material and the over size fraction contains fines.
The following are some of the alternatives that may also solve the hydro-cyclones"" short-circuit problem:
Cyclone Cluster
It consists of a series of two or more cyclones. This results in a lower short-circuit rate, thereby improving the overall efficiency of the operation, but not the efficiency of the individual cyclones. The disadvantages of this solution are: a) an increased investment cost due to the number of cyclones involved; b) an increased operating cost due to the necessary intermediate pumping stages; c) an increased maintenance cost; and d) a more complex overall operation of the system.
Cyclone with Intrusive Apex or Mechanical Insert
It consists of a mechanical insert in the cyclone""s apex. One of the main disadvantages of this solution is that the material used for the intrusive apex is too weak. Usually they should be built using abrasion-resistant, but weak ceramics. However, because the pulp contains metal fragments from the mill balls, bars and liners, they will eventually break and lose their sound classification properties.
Flat Bottom Cyclone
This type of hydro-cyclone does not have the bottom cone that ends in the discharge apex, but the cylindrical body ends in a flat bottom where the apex is inserted. It decreases the short-circuit of fines at discharge of the coarse material, but it increases the discharge or spill of coarse material due to the overflow of fines. While this solution increases the cyclone""s efficiency from a specific throughput point of view, it affects its sharpness as the resulting output has more coarse material than obtained with the traditional cyclone; this results in a lower recovery rate in the flotation process, this aspect being its main disadvantage.
Dual Cyclone with Water Injection
It consists of two cyclone bodies assembled in a single casing with water jets on the apex that dilute the pulp and lower its viscosity, thereby improving its efficiency. The main problem is that it does not allow for the control and regulation of the following operational variables: a) the input velocity ratio between the first and second cyclone; and b) the high pressure required at the intake of the first cyclone to achieve a sound operation of the second cyclone, as otherwise the system will work just like a single cyclone. The technical issue of lack of control of the operational variables in this type of cyclone results in a lower separation efficiency due to poor sharpness index and the lack of control on the cut-off size; thus, one of the present invention""s objectives is to solve this technical problem of the dual cyclone with water injection.
In accordance with the present invention, a dual hydro-cyclone system is provided with a selectively, axially-positionable member located in the region of the bottom of a first hydro-cyclone which provides selective control of the amount of material passing from the first hydro-cyclone to the second hydro-cyclone of the system, thereby providing control of the processing parameters of any given application or use.
The inventor herein, having sought a solution to the technical problems described above with respect to conventional dual hydro-cyclone assemblies, and, after completing different tests and trials has discovered that if:
a) the feeding and discharge of both cyclones"" overflows form a volute in the horizontal plane within the body of the respective cyclone; and
b) the first cyclone, between its bottom and an expansion zone, has an axial positioning adjustable mechanical part or member, the operating variables may be successfully controlled. That is it allows for regulation and control of the intake velocity ratio between the first and second cyclone, and also the pressure at the intake of the first cyclone, thereby resulting in a lower working pressure requirement than that required in the traditional dual cyclone system.